testing of 11kV cable

[hilleard]

Good afternoon all,

Could anyone please tell me of a specific british standard or test procedure I could use as a reference for ensuring the intergrity of a newly installed 11kV cable?

I believe the cables to be installed are EPR Type 4F (BS6195) and run from the outgoing tereminals on an MV generator out to an adjacent "link box".

Many thanks for your help.

 

[wareagle]

Okonite suggests a DC test of 300 volts per mil of insulation. Not sure of the AC requirements.

 

[Strander]

Please see BS 6622 SPECIFICATION FOR CABLES WITH EXTRUDED CROSS-LINKED POLYETHYLENE OR ETHYLENE PROPYLENE RUBBER INSULATION FOR RATED VOLTAGES FROM 3.8/6.6 KV UP TO 19/33 KV .

 

[dualrobin]

In general I have not found a specific BS on the testing of High Voltage cables. However the industry rule of thumb for DC voltage testing is 1.5 x nominal AC voltage.

 

[squasher]

I have found in the past that if you contact the manufacturer of the cable they will advise you on the appropriate test voltages & time period.Also speak to a recognised good MV cable test engineer(s).
The values I have used for 6.35/11kV Cu/XLPE/SWA/PVC cables in practice has been:

5kV "Megger" DC insulation test phase to earth for 2/3 Mins
-cable is glanded both ends -armour is earthed.Phase conductors disconnected both ends, pulled off clear(checks insulation resistance prior to a DC pressure test -
a typical reading would be Gig ohms)

Then do a DC pressure test based on 22kV for 5mins (2 x working voltage).If each phase core is copper screened then a phase to earth test is really only required.You can "strap" all cores together and do what they might call a "one" shot to earth.The leakage on a XLPE should be less than 0.01mA or less,eg negligble.If you get mA you may have got a problem.

Then do a final 5kV megger test,all phase to earth.This should have the same results eg Gigohms,as pre DC pressure test.

Phase conductors are discharged to earth after each of the above tests.
Let me know if you require further info.
Best of Luck

 

[ScottyUK]

There is a BS for this - I think I have a copy in the office. I'll look it up when I get back in.


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Start each day with a smile. Get it over with.

 

[benlanz]

Sorry, I don't have a British standard for cable testing but, I can tell you that a DC test is useless unless you are testing for a failed cable. DC will not find 99% of defects in extruded cable systems (international standards agree or are presently changing). AC HIPOT (2Uo) for one hour is a more reasonable test but you will still miss some defects. The only test that will prove reliability is to repeat the manufacturer’s test in the field -a 50Hz partial discharge test to at least 2Uo.

Cheers,

-Ben


Benjamin Lanz
Vice Chair of IEEE 400
Sr. Application Engineer
IMCORP- Power Cable Reliability Consultants